Pervasive fitness trade-offs revealed by rapid adaptation in large experimental populations of .

Life-history trade-offs are an inherent feature of organismal biology that evolutionary theory posits play a key role in patterns of divergence within and between species. Efforts to quantify trade-offs are largely confined to phenotypic measurements and the identification of negative genetic-correlations among fitness-relevant traits. Here, we use time-series genomic data collected during experimental evolution in large, genetically diverse populations of to directly measure the manifestation of trade-offs in response to temporally fluctuating selection pressures on ecological timescales.

Beneficial reversal of dominance maintains a resistance polymorphism under fluctuating insecticide selection.

Large-effect functional genetic variation is commonly found in natural populations, even though natural selection should erode such variants. Theory suggests that under fluctuating selective pressures, beneficial reversal of dominance - where alleles are dominant when beneficial and recessive when deleterious - can protect these loci from selection, allowing them to persist. However, empirical evidence for this mechanism remains elusive because testing requires direct measurements of selection and dominance in natural conditions.

pigmentation demonstrates adaptive phenotypic parallelism but genomic unpredictability over multiple timescales.

Unlabelled: Populations are capable of responding to environmental change over ecological timescales via adaptive tracking. However, the translation from patterns of allele frequency change to rapid adaptation of complex traits remains unresolved. We used abdominal pigmentation in as a model phenotype to address the nature, genetic architecture, and repeatability of rapid adaptation in the field.

Direct observation of adaptive tracking on ecological time scales in .

Direct observation of evolution in response to natural environmental change can resolve fundamental questions about adaptation, including its pace, temporal dynamics, and underlying phenotypic and genomic architecture. We tracked the evolution of fitness-associated phenotypes and allele frequencies genome-wide in 10 replicate field populations of over 10 generations from summer to late fall. Adaptation was evident over each sampling interval (one to four generations), with exceptionally rapid phenotypic adaptation and large allele frequency shifts at many independent loci.